I see that the TOR project gives the ability to download the list of exit nodes on their site. However, do these IPs change constantly? Would I need to continually download the new list of IPs if I wanted the current list?

Many sites that have Tor exits seem to have more than one. I deal with this by looking up what IP range is assigned to the customer or ISP, then block the entire range to make sure they can't bother me.

Would I be able to get a list of Tor Exits from the main Tor site, or is there another source?
Thanks!